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The accuracy of our MATHCAD generated design parameters is based upon empirical fluidization velocity equations. We developed a bench-scale model of our filtration system and conducted an experiment measuring the expansion of a filter bed as backwash velocity is varied. We then compared the empirically calculated fluidization velocities with the actual fluidization velocities required.
Fluidization Velocity Experiment.

Results and Discussion

Our experiments demonstrate that Okun and Schulz equation for headloss through a fluidized bed is a valid tool to use in our design.

We had mixed results with regards to Weber's equation for filter bed expansion. At low levels of filter bed expansion, the Weber equation accurately predicted the fluidization velocity required to achieve the targeted bed expansion. As the target bed expansion increased, so did the degree of error. At 9% expansion, the degree of error was at 14%. At 38% expansion, the degree of error was at 37%.

We believe the following to be sources of error.

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*Human error: Despite our best attempt at being consistent (by

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measuring and marking heights on the test tube, while also holding a ruler on the test tube wall), there will always be human error in observing the bed expansion visually. The next expansion experiment should use a camera so there is record of the heights at each flow rate, and also tape a ruler to the filtration bed wall, rather than holding the ruler or drawing it on.
*Wall Friction: We can attribute the increase in error as flow rate increased due to the increase in wall friction on the test vial. We can minimize the wall and tube friction by increasing the size of our bench scale experiments.
*Sand Properties Parameters: We might have used an incorrect D60 and porosity for the filter bed in our equations. For the next experiment those parameters should be found out for the sand or material used by using a sieve.
*Preferential flow: Despite our best attempt to keep the test tube as level as possible, we might have introduced preferential flow in our experiment causing an unbalanced backwash flow. In the future, two levels could be clamped on the sides of the filter walls to ensure it is level. A further precaution would be to use two clamps, rather than one.
*Expansion Headloss: The accuracy of our model also required the headloss occurring through the expanded bed to be more or less constant, which we did not have time to test (but is part of Recommended Future Research below).

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Testing it would involve putting a pressure sensor into the system, connected on either end of the filter.

Recommended Future Research

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